On Friday night, comedian Bill Maher had a controversial guest on his show: Samir Chachoua, an Australian doctor who practices in Mexico. Earlier this month, Charlie Sheen went on The Dr. Oz Show and described going to Mexico to get Chachoua’s unproven HIV treatment, injections he developed after studying the milk of goats with arthritis.

Doctors and HIV/AIDS experts are shocked that Maher would promote such adubious medical treatment to his HBO show’s audience of 4 million people.

“I was absolutely flabbergasted,” Mark Harrington, executive director of Treatment Action Group, a New York-based HIV advocacy organization, told BuzzFeed News. “To promote a quack on his show as someone who could even diagnose symptoms of HIV, it’s very irresponsible and can only be described as tabloid journalism at its worst.”

“This kind of high profile pumping of alternative medicine stories linked to celebrities can harm other people by persuading them to do damaging things that affect their health,” John Moore, a professor of microbiology and immunology at Weill Cornell Medical College in New York, told BuzzFeed News.

“This is a classic example of false hope syndrome,” Moore added. “People are persuaded to do wacky stuff that stops them from doing the right stuff.”

Maher’s representative did not respond to a request for comment.

Chachoua did not respond to a request for comment, but he posted a long response to Oz and Sheen on his website, in which he stands by his claims. He also alleged there that Sheen initially came to him to “make his law suits go away by offering a treatment to people that he may have infected.”

Sheen’s manager, Mark Burg, vehemently denies this claim.

“None of it is true, sad what some people will do to make money,” Burg told BuzzFeed News by email. “Charlie will respond when he next does the Dr. Oz show on Feb 9.”